a) Field of the Invention
The invention is directed to a flexible connection arrangement for two pipe portions, particularly in motor vehicle exhaust systems, with a metallic bellows which is connected axially on either side in a gastight manner with connection pieces in the form of substantially cylindrical sleeves or sockets, the sides of the connection pieces facing the bellows having radially widened end portions with substantially cylindrical end regions, the connection arrangement further comprising a damping insert, which extends coaxially to the bellows along its length and is in a working connection therewith, and heat protection means for the bellows acting in the radially inward direction.
b) Description of the Relevant Art
Such flexible connection arrangements are used in exhaust systems, particularly in motor vehicles, in the form of intermediate pieces serving to connect the pipe portions attached thereto in a resilient, articulated and damped manner and to eliminate vibrational interaction between these parts, i.e. to uncouple relative movements, oscillations and vibrations from the adjacent structural component parts. In other respects, the exhaust lines are constructed as rigid systems so that the matter of resilient uncoupling is of considerable importance.
With regard to connection arrangements of this type, increasing attention has lately been centered on questions relating to good sound-proofing, effective heat insulation and, in particular, efficient sealing against undesirable emission of exhaust gases from the exhaust line, particularly if the connection arrangements in question are installed upstream of the catalytic converter as viewed in the direction of flow of the exhaust gases.
A great many flexible connection arrangements of this type for pipe portions are known, including those in which sealing against unwanted emission of exhaust gases is effected by means of a metallic bellows whose two ends are tightly connected, respectively, with the two pipe portions.
A flexible connection arrangement which makes use of a flexible bellows directly surrounded by a braided tube of metal wire is known from EP-A-0 432 436. The bellows and braided tube are arranged inside a cylindrical support ring and pressed together with one another and with the latter at the ends, the parts being interconnected by provisional stitches. In addition, at least one flexible damping member which proceeds from one end of the connection arrangement and is movable relative to the braided tube is provided for effectively absorbing the oscillations and vibrations occurring during operation. The damping member produces the desired damping action by frictional contact with the braided tube surrounding the bellows. For example, this flexible damping member may be constructed as a spring (e.g., a coil spring or helical spring) which has frictional contact with and is displaceable on the braided tube, one end of the spring being fastened to an end of the connection arrangement, while its other end is arranged on the braided tube so as to be freely displaceable. This known connection arrangement has a somewhat complicated design, since both axial ends of the braided tube must be tightly and securely pressed together with the respective ends of the bellows and supporting ting. Moreover, the braided tube must completely absorb all axial forces, which can result in a tear in its connection points at the ends or even in the braided tube itself. In addition, such metallic braided tubes have only a very limited ability to rotate and become frayed easily. It is also difficult to assemble known connection arrangements of this type, particularly as concerns the frictional contact of the damping spring at the braided tube.
A flexible connection arrangement of the type mentioned in the introduction is described in EP 0 282 689 A2. In this known flexible connection element, the bellows and damping insert are arranged coaxially relative to one another, the radially inwardly directed end regions of the folds of the bellows being embedded in the damping insert to a certain penetration depth. The working connection thus achieved between the damping insert and the convolutions or turns of the bellows results in a very efficient damping of oscillations in the bellows and a uniform distribution of oscillations along the entire length of the bellows. In addition, the damping insert acts at the same time as an insulating layer and as heat protection means acting toward the inside of the bellows. For this purpose, the radial inner surface of the damping insert is formed by a metal tube in the form of a clasp sleeve which is arranged coaxially to the damping insert and is welded at both ends inside the inner circumference of one of the two pipe portions to be connected. The outside of the bellows is enclosed by a braided metal tube for external protection against mechanical damage and dirt. In the region of its outer diameter, the ends of the metal bellows are welded to the radially widening end portions of the closing ends along with the tube enclosing the bellows. The known flexible connection arrangement provides complete sealing of the connection points with good sound insulation and heat insulation. However, the known connection element has a very complicated design and requires four circumferential welds, two of which serve to fasten the tube, bellows and connection piece simultaneously. Specifically welds of this type could easily lead to warping or distortion and to welding stresses which affect both the bellows and the metallic tube enclosing it and generate positive tensions, for example, which can also result in impaired operation particularly in sensitive metallic bellows. Owing to its complicated design, this known flexible connection arrangement is also relative cumbersome and difficult to assemble. Axial forces must also be absorbed entirely either by the inner metallic tube or by the outer metallic tube surrounding the bellows, which can lead to cracks in the welds or tearing of the metallic tube in question when considerable axial relative movements occur between the metallic parts to be connected. These metallic tubes also have only a very limited elongation capacity and fray easily.